Showing papers in "Journal of Dental Research in 1990"
TL;DR: A clinically practical method of maintenance of the tooth under a continuous stream of argon while being cured in room air was shown to provide greater monomer conversion than curing under room-air conditions alone.
Abstract: Oxygen is known to inhibit vinyl polymerization in resins used for restorative dentistry. This research examined the effects of unfilled resin being blown into a thin layer on etched bovine enamel in atmospheres of room air, argon, or a combination of the two. Onto this thin, cured resin surface, filled resin was added and cured under atmospheric conditions similar to those of the initial polymerization of the unfilled resin. Comparison of the effects of the different testing atmospheres was made by measurement of the shear bond strength of the resin/composite disc to the etched bovine enamel. Monomer conversion values of the unfilled resin were calculated from the infrared spectra of the simulated tooth/disc assembly. Blowing unfilled resin with compressed room air prior to curing caused poor monomer conversion values and resulted in low shear bond strength to etched enamel. Both high monomer conversion and shear strength values resulted when specimens were cured under all-argon conditions. A clinically ...
437 citations
TL;DR: Reduction of the total stiffness by application of an intermediate layer can render the total restoration sufficiently flexible to compensate for that part of the stress that would otherwise exceed the bond strength.
Abstract: The use of adhesive resin composites for restoration of Class V lesions often results in cervical marginal gap formation due to polymerization contraction. In this laboratory study, flexible linings applied between the bonding agent and the bulk restorative appeared to preserve the marginal integrity of Class V restorations during curing. Measurements of the polymerization contraction stress showed 20 to 50% relief due to various flexible intermediate materials. Apparently, reduction of the total stiffness by application of an intermediate layer can render the total restoration sufficiently flexible to compensate for that part of the stress that would otherwise exceed the bond strength.
356 citations
TL;DR: Levels of mutans streptococci in plaque samples from margins of Class II amalgam (Dispersalloy), composite (P-10), and glass-ionomer (Ketac Silver) restorations were compared and the ages of the children, the age of therestorations, and the salivary levels were comparable in the three groups.
Abstract: Levels of mutans streptococci in plaque samples from margins of Class II amalgam (Dispersalloy), composite (P-10), and glass-ionomer (Ketac Silver) restorations were compared. Fifty-one children, each having one of the restorations in a permanent first molar, were part of an inter-individual comparison, giving 17 restorations of each material. The age of the children, the age of the restorations, and the salivary levels of mutans streptococci were comparable in the three groups. Another seven children--each having both a composite and a glass-ionomer restoration of the same age placed on contralateral premolar or molar teeth--were part of an intra-individual comparison. The percentage mutans streptococci of total CFU count in plaque was higher on composite (mean 13.7) and amalgam (mean 4.3) than on glass-ionomer (mean 1.1) restorations in the inter-individual comparison, and higher on composite (mean 4.2) than on glass-ionomer (mean 0.4) restorations in the intra-individual comparison. In both comparisons, the differences in values between samples from glass-ionomer restorations and samples from composite or amalgam restorations were statistically significant (p less than 0.05).
311 citations
TL;DR: The results showed that hydroxyapatite was the only reaction product; the reaction was nearly completed within four h, during which both the reaction product and compressive strength increased linearly with time, resulting in a strong correlation between the two.
Abstract: Setting reactions and compressive strengths of a self-hardening calcium phosphate cement (CPC) were investigated. The CPC consists of tetracalcium phosphate (TTCP) and anhydrous dicalcium phosphate (DCPA). The cement specimens were prepared by mixing 0.7 g of the powder (TTCP 72.9 wt% + DCPA 27.1 wt%) with 0.175 mL of the liquid (25 mmol/L H3PO4 and 1.32 mmol/L sodium fluoride). The specimens were removed from the molds at pre-determined time intervals after being mixed, and their compressive strengths were measured. Immediately afterward, the fractured specimens were rapidly frozen in ethanol (-80 degrees C), lyophilized, and examined by powder x-ray diffraction and scanning electron microscopy (SEM). The results showed that (1) hydroxyapatite was the only reaction product; (2) the reaction was nearly completed within four h, during which both the reaction product and compressive strength increased linearly with time, resulting in a strong correlation between the two; and (3) fully set CPC consisted primarily of small rod-like crystals and some platy crystals.
308 citations
TL;DR: There is no general agreement that the anti-microbial effects of F contribute to the Anticaries effect of fluoride, but the resolution of this question will require new information on the nature and concentration of F in plaque, the minimal level of F required to provide an Anticary effect, and the influence of cellular integrity and activity on F uptake and accumulation by plaque bacteria.
Abstract: Fluoride inhibition of carbohydrate metabolism by the acidogenic plaque microflora is well-established, although it has not always been appreciated that oral bacteria vary considerably in their susceptibility to fluoride. Early studies demonstrated that the F-induced reduction in acid production was due, in part, to the inhibition of the glycolytic enzyme, enolase, which converts 2-P-glycerate to P-enolpyruvate. The decreased output of PEP in the presence of F, in turn, results in the inhibition of sugar transport via the PEP phosphotransferase system (PTS). Bacterial accumulation of fluoride involves the transport of HF, a process requiring a transmembrane pH difference or pH gradient, which is generated only by metabolically active cells. The uptake of HF into the more alkaline cytoplasm results in the dissociation of HF to H+ and F- and, if allowed to continue, the accumulation of protons acidifies the cytoplasm, causing a reduction in both the proton gradient and enzyme activity. Current information indicates that in addition to enolase, F- also inhibits the membrane-bound, proton-pumping H+/ATPase, which is involved in the generation of proton gradients through the efflux of protons from the cell at the expense of ATP. Thus, fluoride has the dual action of dissipating proton gradients and preventing their generation through its action on H+/ATPase. The collapse of transmembrane proton gradient, in turn, reduces the ability of cells to transport solutes via mechanisms involving proton motive force. In spite of these known effects on the bacterial cell, there is no general agreement that the anti-microbial effects of F contribute to the anti-caries effect of fluoride.(ABSTRACT TRUNCATED AT 250 WORDS)
299 citations
TL;DR: The results demonstrate that the strength of zinc phosphate cement depends not only upon the geometric factors, but also upon sample preparation conditions.
Abstract: A bi-axial flexure test (piston-on-three-balls), a four-point flexure test, and a diametral tensile test were used to measure the failure stress of four brittle dental materials: zinc phosphate cement, body porcelain, opaque porcelain, and visible light-cured resin composite. Furthermore, the fracture probability of the bi-axial test specimens was predicted from the results of the four-point flexure test, with use of statistical fracture theory. Bi-axial failure stresses calculated from an equation developed by Marshall (1980) exhibited no significant difference for zinc phosphate cement as a function of piston size, specimen thickness, presence or absence of a stress-distributing film, and loading rate. The four-point flexure strength values of zinc phosphate cement and opaque procelain were significantly lower (p less than 0.05) than the corresponding mean bi-axial strength values, while the mean four-point flexure strength values of body porcelain and resin composite were not significantly lower (p greater than 0.05) than the corresponding mean bi-axial strength values. The diametral tensile strength of all materials was significantly lower than the bi-axial flexure strength. The mean bi-axial flexure strengths of zinc phosphate cement and opaque porcelain were much higher than the theoretical values predicted from surface flaw theory, while the strength values for body porcelain and resin composite were comparable with those determined from the four-point flexure test. These results demonstrate that the strength of zinc phosphate cement depends not only upon the geometric factors, but also upon sample preparation conditions.
277 citations
TL;DR: For the in vivo patterns and the effects of caries-preventive substances to be studied, de- and remineralization can best be examined with a pH-cycling system in which the pH depressions occurring in the oral environment are mimicked in a laboratory model.
Abstract: The recent literature extensively describes the role of ambient fluoride in the de- and remineralization of dental enamel. Fluoride in sub-ppm concentrations is effective in promoting mineral deposition and inhibiting mineral dissolution. The latter phenomenon is most likely attributable to the concomitant precipitation of a fluoride-rich mineral phase which inhibits further dissolution. These fundamental processes result in an inhibition of enamel demineralization and an enhancement of enamel lesion remineralization. Alternatively, fluoride may also induce the 'arrestment' of enamel lesions. For the in vivo patterns and the effects of caries-preventive substances to be studied, de- and remineralization can best be examined with a pH-cycling system in which the pH depressions occurring in the oral environment are mimicked in a laboratory model. Such an approach has proved useful in developing optimal fluoride schemes which can be tested in animal, intraoral, and clinical studies.
256 citations
TL;DR: The results suggest that water fluoridation has played a dominant role in the decline in caries and must continue to be a major prevention methodology.
Abstract: The decline in dental caries in U.S. schoolchildren, first observed nationwide in 1979-1980, was confirmed further by a second national epidemiological survey completed in 1987. Mean DMFS scores in persons aged 5-17 years had decreased about 36% during the interval, and, in 1987, approximately 50% of children were caries-free in the permanent dentition. Children who had always been exposed to community water fluoridation had mean DMFS scores about 18% lower than those who had never lived in fluoridated communities. When some of the "background" effect of topical fluoride was controlled, this difference increased to 25%. The results suggest that water fluoridation has played a dominant role in the decline in caries and must continue to be a major prevention methodology.
254 citations
TL;DR: It can be demonstrated that there is a linear association between fluoride dose and dental fluorosis (r2 = 0.87), and it is concluded that it is important to intensify studies on factors which alone or in combination can make individuals more or less susceptible to the effect of fluoride.
Abstract: Any use of fluorides, whether systemic or topical, in caries prevention and treatment in children results in ingestion and absorption of fluoride into the blood circulation. The mineralization of teeth under formation may be affected so that dental fluorosis may occur. Dental fluorosis reflects an increasing porosity of the surface and subsurface enamel, causing the enamel to appear opaque. The clinical features represent a continuum of changes ranging from fine white opaque lines running across the tooth on all parts of the enamel to entirely chalky white teeth. In the latter cases, the enamel may be so porous (or hypomineralized) that the outer enamel breaks apart posteruptively and the exposed porous subsurface enamel becomes discolored. These changes can be classified clinically by the TF index to reflect, in an ordinal scale, the histopathological changes associated with dental fluorosis. Compared with Dean's and the TSIF index, we consider the TF index to be more precise. Recent studies on human enamel representing the entire spectrum of dental fluorosis have demonstrated a clear association between increasing TF score and increasing fluoride content of the enamel. So far, no useful data on dose (expressed in mg fluoride/kg b.w.)-response (dental fluorosis) relationships are available. In this paper, we have, therefore, re-evaluated the original data by Dean et al. (1941, 1942), Richards et al. (1967), and Butler et al. (1985) from the USA, by applying the equation of Galagan and Vermillion (1957) which permits the calculation of water intake as a function of temperature.(ABSTRACT TRUNCATED AT 250 WORDS)
244 citations
TL;DR: Clinical implications are that simply increasing fluoride concentration may not necessarily give increased cariostatic benefit, and that improving the means of delivery of relatively low fluoride concentrations for longer times should be more appropriate for enhancing clinical efficacy.
Abstract: The anti-caries activity of fluoride is contributed to in several ways. Two major aspects of fluoride action are (i) the inhibition of demineralization at the crystal surfaces within the tooth, and (ii) the enhancement of subsurface remineralization resulting in arrestment or reversal of caries lesions. Fluoride present in the aqueous phase at the apatite crystal surface may play a determining role in the inhibition of enamel or dentin demineralization. In one part of the present study, the initial dissolution rate of synthetic carbonated-apatite in acetate buffers was measured with fluoride present in the buffer in the 0-2.6 mmol/L (0-50 ppm) range. Inhibition of demineralization was shown to be a logarithmic function of the fluoride concentration in solution. In the second part of the present study, an in vitro pH-cycling model was used for determination of the effect on net de/remineralization of enamel by treatment solutions containing fluoride in the 0-26 mmol/L (0-500 ppm) range. The net mineral loss was shown to be negatively related to the logarithm of the fluoride concentration. These studies have demonstrated an exponential quantitative relationship between fluoride concentration and inhibition of apatite demineralization or enhancement of remineralization. The clinical implications are (i) that simply increasing fluoride concentration may not necessarily give increased cariostatic benefit, and (ii) that improving the means of delivery of relatively low fluoride concentrations for longer times should be more appropriate for enhancing clinical efficacy.
229 citations
TL;DR: The purpose of this epidemiological study was to estimate the degree of change in periodontal attachment level in a sample of adults examined in 1959 and 1987 in Tecumseh, Michigan, and the individuals with high LPA increase had the following characteristics significantly different from those with low LPA rise: age, smoking, and presence of tooth mobility.
Abstract: The purpose of this epidemiological study was to estimate the degree of change in periodontal attachment level in a sample of adults examined in 1959 and 1987 in Tecumseh, Michigan. Out of 526 individuals between the ages of five and 60 years in 1959, a sample of 325 resided within an 80-km-radius area in 1987. Of those, 167 were re-examined. Loss of periodontal attachment (LPA) was determined with a Michigan #0 probe on four tooth sites (disto-buccal, mid-buccal, mesio-buccal, mid-lingual) for all teeth present. Of the individuals contacted, 28 had lost all their teeth during the 28 years. Of the 167 adults examined, two refused periodontal probing. Out of the 165 adults with LPA measurements in 1987, only 22 (13.3%) had an average increased loss of 2 mm or more per person between 1959 and 1987; five adults (3.0%) had an average LPA increase of 3 mm or more, and only two adults (1.2%) had an average LPA increase of 4 mm or more. The attachment level in 59.3% of all the tooth sites examined in 1959 in the...
TL;DR: Evaluating a new color-difference equation provides a means for estimation of AE CIE L*a*b* color difference between dental shades with Munsell notation, which will be useful for estimations of small AECIE L-a-b* values for shade-guide teeth that are designated in terms of Munsel notation.
Abstract: Traditionally, dental-shade-guide standards are designated in terms of Munsell hue (H), value (V), and chroma (C). However, delta E color differences proposed as ADA tolerances for shade guides are in the CIE L*a*b* system. The purpose of this study was to evaluate a new color-difference equation, delta EM = C delta H/5 + 7 delta V + 4 delta C for estimation of small color differences by Munsell parameters. The published values of the Bioform shade-guide tooth colors determined with a Beckman spectrophotometer were used. Color differences among 276 combinations of the 24 Bioform shade-guide colors were calculated with Eq. 1, with use of the Munsell notation, and also with the CIE L*a*b* equation for delta E. An estimate of the accuracy of Eq. 1 was 0.41 delta E units when delta E CIE was below 4.0. The Vita shade-guide colors were determined with a Beckman spectrophotometer. This data set contained 16 samples, and 120 combinations were used for calculation of color difference. An estimate of the accuracy for this set of data was 0.35 delta E units when delta E CIE was less than 4.0. The new color-difference equation provides a means for estimation of delta E CIE L*a*b* color difference between dental shades with Munsell notation. This equation will be useful for estimation of small delta E CIE L*a*b* values for shade-guide teeth that are designated in terms of Munsell notation.
TL;DR: A reduction in pH of the agents is probably the most practical approach to increase the deposition of calcium fluoride during topical application, and clinical data support this contention.
Abstract: There is evidence that a major part of the fluoride which is retained on teeth during topical application is calcium fluoride or calcium fluoride-like, and that this material is relatively stable in the mouth. This is due to surface adsorption of phosphate (HPO4(2-)) ions onto the calcium fluoride surface. Calcium fluoride releases fluoride during caries challenges due to reduced concentration of HPO4(2-) at acid pH. Normally, the fluoride released from calcium fluoride during caries challenges is subsequently built into hydroxyfluorapatite through dissolution/re-precipitation reactions. It appears likely that the formation of calcium fluoride from topical application agents should be increased and not reduced, as believed in the past. Increased deposition of calcium fluoride can be achieved with increased reaction time between fluoride and enamel, reduced pH of the solution, increased concentration, or pre-treatment with calcium. A reduction in pH of the agents is probably the most practical approach to increase the deposition of calcium fluoride during topical application, and clinical data support this contention. Calcium fluorides with various dissolution rates are formed during different procedures of topical application with fluoride, presumably due to incorporation of phosphate into the calcium fluoride crystals.
TL;DR: Evidence suggests that there is a strong association between mild to moderate enamel fluorosis and the use of fluoride supplements during early childhood, and that the presently recommended supplementation schedule for U. S. children above the age of 2 years may be too high.
Abstract: Recent studies indicate that the prevalence of very mild to moderate dental fluorosis, as classified by Dean, has increased relative to that found in earlier investigations. To date, fluoridated water, fluoride supplements, the diet, fluoride dentifrices, and other topical fluoride applications have been identified as sources of systemic fluoride. Recent evidence suggests that there is a strong association between mild to moderate enamel fluorosis and the use of fluoride supplements during early childhood, and that the presently recommended supplementation schedule for U.S. children above the age of 2 years may be too high. Evidence also suggests that there is a strong association between fluoride dentifrice use during early childhood and enamel fluorosis in fluoridated populations. These findings support the need for a careful review of existing supplementation schedules and early oral hygiene practices. There is a pressing need for additional analytical epidemiological studies to confirm existing findings and to determine whether other fluoride sources may be associated with enamel fluorosis. Further, since exposure to combinations of individual risk factors has been shown to carry more than merely an additive increase in the risk of fluorosis, these studies must be multifactorial in design. There is also a need for more fluorosis prevalence and severity data to be gathered, so that the development of enamel fluorosis as a public health problem can be assessed, and so that the success of measures implemented to maximize efficacy while minimizing unwanted side-effects can be monitored.
TL;DR: These results establish, for the first time, the complete structural relationships between all members of this group of microbicidal proteins in human parotid saliva.
Abstract: Histatins are a group of electrophoretically distinct histidine-rich polypeptides with microbicidal activity found in human parotid and submandibular gland secretions. Recently, we have shown that histatins 1, 3, and 5 are homologous proteins that consist of 38, 32, and 24 amino acid residues, respectively, and that these polypeptides kill the pathogenic yeast, Candida albicans. We now describe the isolation and structural characterization of histatins 2, 4, 6, and 7-12, the remaining members of this group of polypeptides. Histatin 2 was found to be identical to the carboxyl terminal 26 residues of histatin 1; histatin 4 was found to be identical to the carboxyl terminal 20 residues of histatin 3; and histatin 6 was found to be identical to histatin 5, but contained an additional carboxyl terminal arginine residue. The amino acid sequences of histatins 7-12 formally correspond to residues 12-24, 13-24, 12-25, 13-25, 5-11, and 5-12, respectively, of histatin 3, but could also arise proteolytically from his...
TL;DR: From the measured deflections, the maximum tangential bending stress in the resins near the adhesive interface was calculated, which provided an estimation for the maximum shear stress values occurring at both ends of the strips.
Abstract: We studied relaxation by hygroscopic expansion of the interfacial polymerization shear stress of bonded resin composites. In the experimental set-up, resin composite-cured-to-glass strips bent due to the polymerization shrinkage. The strips were stored wet or dry. The curvatures of the bent strips were recorded, by the scanning of the glass surfaces with a contact profilometer, periodically over a period of two months. From the measured deflections, we calculated the maximum tangential bending stress in the resins near the adhesive interface, which provided an estimation for the maximum shear stress values occurring at both ends of the strips. In the particular experimental set-up, the shear stresses in Bis-GMA/TEGDMA and urethane dimethacrylate-based resins were either fully relieved or converted into an "expansion stress" by hygroscopic expansion. The hydrophobic tricyclodecane dimethacrylate-based resins showed very little stress relaxation.
TL;DR: It is concluded that non-dietary sources of fluoride, mainly fluoride-containing dental products, are a major source of ingested fluoride.
Abstract: The metabolism and toxicity of fluoride are discussed with emphasis on new scientific findings. The gastric absorption, tissue distribution, and renal excretion of the ion are all influenced by the magnitude and direction of the pH gradient between adjacent body fluid compartments. This mechanism explains the asymmetric distribution of fluoride across cell membranes, and the manipulation of transmembrane pH gradients has proven efficacious in acute fluoride toxicity. The comparative metabolism and relative toxicities of ionic fluoride and monofluorophosphate are discussed. It is no longer certain that there is a difference between the acute toxic potentials of sodium fluoride and those of MFP. It is concluded that the "probably toxic dose" or PTD of fluoride--the dose which should trigger therapeutic intervention and hospitalization--is 5 mg/kg of body weight. As currently packaged, many dental products contain sufficient fluoride to exceed the PTD for young children. There is a need for additional research into the sources, effects, and fate of strongly bound or organic fluoride compounds. Attention is drawn to the fact that, while the metabolic characteristics and effects of fluoride in young and middle-aged adults have received considerable research attention, there is a paucity of such information for young children and the elderly. The increasing prevalence of dental fluorosis is addressed. It is concluded that nondietary sources of fluoride, mainly fluoride-containing dental products, are a major source of ingested fluoride. The article concludes with 12 recommendations for future research.
TL;DR: While the analysis had to be carried out without caries data, it was concluded that total tooth loss is a social-behavioral issue as much as it is disease-related.
Abstract: Over 500 residents of Tecumseh, Michigan, were dentially examined in 1959 as part of a community-wide health study. In 1987, the dental examinations were repeated, with use of the same criteria as in 1959, for 167 dentate persons from the original group. Another 28 reported by telephone that they had become edentulous since 1959. This report uses a historical cohort analysis for exploration of the risk factors for tooth loss, both total and partial, over the 28-year period. Over that time, the edentulous lost an average of 18.0 teeth (95% confidence interval 15.5, 20.7), whereas the age-matched 90 dentate persons lost only 3.2 (2.2, 4.2) teeth each. Descriptive data showed the edentulous to have higher baseline scores for plaque, calculus, and gingivitis, and a higher proportion of them smoked, though only loss of periodontal attachment (LPA) of 4 mm or more, early loss of first molars, and educational attainment were significant risk factors in regression analysis. Odds ratios for these three variables were 4.0 (1.2, 12.8), 2.0 (1.3, 3.1), and 0.6 (0.4, 0.9), respectively. The strongest risk factors for partial tooth loss among 116 dentate persons were baseline gingivitis (which was correlated with LPA of 4 mm or more) and the baseline number of teeth present, with odds ratios of 2.4 (1.2, 5.2) and 0.8 (0.7, 1.0), respectively. While the analysis had to be carried out without caries data, it was concluded that total tooth loss is a social-behavioral issue as much as it is disease-related. Social-behavioral factors were less clearly related to partial tooth loss in dentate persons; oral disease characteristics were the most prominent risk factors for partial tooth loss.
TL;DR: It is concluded that the benefits provided by water fluoridation result, to a large degree, from a topical effect and it is suggested that clinical procedures be developed to establish and maintain low levels of free fluoride in plaque fluid.
Abstract: The cariostatic mechanisms of systemic and topical fluoride agents are considered in light of a previously proposed model for the caries process. It is noted that fluoride, in principle, can induce a cariostatic effect: by (1) reducing enamel solubility when incorporated into the mineral structure; (2) by fostering the remineralization of incipient enamel lesions and the deposition of fluoridated phases (within dental plaque) which provide a source of mineral ions (Ca, P, F) under acidic conditions; and (3) by reducing the net rate of transport of matter out of the enamel surface, under acidic conditions, by inducing the reprecipitaion of fluoridated hydroxyapatite phases within enamel. It is also noted that relatively high (~ 12,000 ppm) concentrations of professionally applied topical fluorides significantly reduce the rate of acid production of cariogenic organisms (e.g., S. mutans). Based on an analysis of available clinical and laboratory data, it is concluded that the benefits provided by water fluo...
TL;DR: It has been known for 17 years that the Actinomyces associated with the lesions may be variants of A. viscosus and A. naeslundii, and recent studies suggest that this is so, since samples from root surface lesions which contain S. mutans and Lactobacillus show a high isolation of S. Mutans.
Abstract: Studies on the microbiology of root surface caries between 1970 and 1975 placed emphasis on Gram-positive pleomorphic filamentous rods, particularly Actinomyces viscosus and Actinomyces naeslundii. Both of these species had been shown to produce root surface caries in experimental animals. Since this time, studies have placed more emphasis on Streptococcus mutans, and S. mutans and Lactobacillus are significant in prediction of root surface caries risk in patients. Subsequent studies confirmed an association between S. mutans and 'soft' or 'initial' root lesions. Thus, it is important when determining the microflora of root surface lesions to make careful characterization of the state of the lesion. A second important aspect of the analysis of bacterial communities associated with root surface caries is better definition of the organisms. Most studies have concentrated on 'target organisms' S. mutans, S. sanguis, A. viscosus, A. naeslundii, Lactobacillus, and Veillonella. However, it has been known for 17 years that the Actinomyces associated with the lesions may be variants of A. viscosus and A. naeslundii. Such strains (intermediate strains) have been described in taxonomic studies of Actinomyces, yet little is known of the differences in physiology of these strains or their relationship to root surface caries. A similar situation exists with oral Streptococcus where new taxonomic divisions are being proposed. Recognition of the potential diversity within the 'target' genera of root surface caries could yield valuable data. Recent studies suggest that this is so, since samples from root surface lesions which contain S. mutans and Lactobacillus show a high isolation of S. mitis 1 and no isolations of A. naeslundii. Careful definition of the lesions of root surface caries and the flora will allow analysis to relate a specific bacterial community to the state fo the lesion and assist in monitoring the control of the lesion through fluoride and antibacterials.
TL;DR: It is shown that water has an irreversible effect on most dental composites and some products within Group III did not show any tendency to recover their strength after dehydration.
Abstract: The objective of this study was to investigate whether water storage causes permanent damage to composites by determining how the tensile strength of nine different composite materials changes with both water storage and water storage followed by dehydration. Eighteen samples (ASTM-D Specification 1708-66) of each of the nine materials were prepared and divided into three groups of six samples each. Group I was stored dry at 60°C, while Groups II and III were stored in distilled water at 60°C. After six months, Groups I and II were subjected to tensile testing, while Group III was transferred to a desiccator and dehydrated for two weeks at 60°C before this group was tested in tension. Mean values, pooled by storage group independent of material, revealed a significant (p<0.05) reduction in strength for both Groups II and III relative to Group I. These findings prove that water has an irreversible effect on most dental composites. A comparison of Group II with Group III data revealed that the samples which...
TL;DR: The bonding of an experimental low-fusing porcelain to titanium and Ti-6AI-4V was evaluated by an x-ray spectrometric technique that measures the area that remains covered with Porcelain following a controlled deformation of the metallic substrate.
Abstract: The bonding of an experimental low-fusing porcelain to titanium and Ti-6AI-4V was evaluated by an x-ray spectrometric technique that measures the area that remains covered with porcelain following a controlled deformation of the metallic substrate. Oxide adherence strength values for titanium and Ti- 6AI-4V oxidized at 750° and 1000°C were measured in tension with use of high-strength adhesives. The effect of further oxidation that would occur during porcelain firing was evaluated via simulated porcelain firings without actual porcelain application. Interface cross-sections of the titanium-porcelain and Ti-6AI-4V-porcelain bonds were examined in a scanning electron microscope (SEM). The porcelain was found to delaminate completely from the metal substrate, leaving less than 1% of the surface covered with porcelain. The oxide adherence of the specimens oxidized at 750°C was good, but those oxidized at 1000°C exhibited significantly lower oxide adherence (p = 0.001). The simulated porcelain-firing oxidation...
TL;DR: This review examines the literature on the interactions of saliva with taste, and the effect of taste on salivary composition and the possible role of the von Ebner'ssalivary glands.
Abstract: In spite of the coexistence of saliva and taste in the oral cavity, an understanding of their interactions is still incomplete. Saliva has modulating effects on sour, salt, and the monosodium-glutamate-induced savory or umami taste. It has a diminishing effect on sour taste as a result of the buffering by salivary bicarbonate. It probably also contributes to the umami taste with endogenous salivary glutamate levels. Salt taste is detected only when above salivary sodium-chloride concentrations; thus saliva influences salt taste threshold levels. It also provides the ionic environment for taste cells, probably critical in signal transduction. Salivary flow rate and composition are influenced by the type of taste stimuli. In general, sour taste, elicited by citric acid or sour food, induces the highest flow rate and Na+ concentrations, while salt gives rise to high protein and Ca2+ concentrations. Stimulation with the four basic taste modalities (sour, sweet, salty, and bitter), however, does not increase the relative proportion of any of the salivary proteins. This review examines the literature on the interactions of saliva with taste, and the effect of taste on salivary composition. The possible role of the von Ebner's salivary glands and the role of saliva as a chemical cue are also discussed.
TL;DR: It is indicated that frequent low-level applications of fluoride are most likely more beneficial in caries prevention than few treatments with solutions having a high fluoride concentration.
Abstract: This paper discusses loosely bound fluoride and its role in dental caries and prevention. Loosely bound fluoride (abbr. by Fa) is fluoride adsorbed onto enamel mineral crystallites. Several recent studies indicate that a high total level of fluoride in enamel does not guarantee protection against caries. This leads to the conclusion that a major part of fluoride present in the solid enamel is not active in prevention. The adsorption of Fa to the mineral under acidic conditions is described. Most likely there is a dynamic equilibrium between fluoride in solution and adsorbed Fa at the crystal surface interface. When the crystallite is completely covered by adsorbed Fa, there is a maximum inhibition of dissolution. The rate of dissolution of mineral depends on pH, the actual concentrations of calcium and phosphate in the liquid in contact with the crystallites, and on the fraction of the surface covered by adsorbed fluoride. The fluoride, Fs, localized in the inner part of the crystallites is relatively unimportant. "CaF2-like" material can be formed on and in enamel depending on conditions. The in vivo-formed globular "CaF2-like" material is not pure CaF2 and releases F- ions when dissolving; these ions will also be partly adsorbed as Fa in and on enamel. Presently, the amount and importance of Fa originating from in vivo-formed "CaF2-like" material are not known. The level of fluoride, Fa, necessary for strong inhibition of enamel demineralization in vitro is estimated to correspond to a fluoride concentration, FL, in the liquid phase of 1 ppm or 50 mumol/L fluoride ions.(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: The effects of filler concentration and resinous components on the properties of highly filled composites were determined for prediction of the durability of the restorative resins.
Abstract: The effects of filler concentration and resinous components on the properties of highly filled composites were determined for prediction of the durability of the restorative resins. Resinous components of seven proprietary light-cured posterior resin composites were extracted by chloroform solvent and examined by the Fourier Transform Infrared (FTIR) method. Filler concentration was determined by the thermogravimetric method. Diametral tensile strength, Knoop hardness, and Barcol hardness tests for the composite, as well as extracted resinous matrix, were performed by standard experimental procedures. Toothbrush abrasion test of the resin composites was evaluated by a toothbrushing machine giving the equivalent of five years' toothbrushing and examined with a roughness meter. The degree of conversion of resin composites ranged from 43.5 to 73.8%. The volume fraction of filler varied from 58.2% to 74.2%. The ranges of diametral tensile strength and Knoop and Barcol hardness numbers obtained were 39.8 MPa t...
TL;DR: The aim was to obtain a more representative estimation of the daily dose of mercury vapor inhaled from amalgam fillings by measurement of amounts of Mercury vapor released in the oral cavity during 24 h, under conditions that were as normal as possible.
Abstract: The difficulties associated with estimations of daily doses of inhaled mercury vapor released from dental amalgam are considerable. Existing data are often unreliable, especially if they are based on a single or a small series of samples of intra-oral concentrations of mercury vapor before, during, and after chewing stimulation. In the present paper, the aim was to obtain a more representative estimation of the daily dose of mercury vapor inhaled from amalgam fillings by measurement of amounts of mercury vapor released in the oral cavity during 24 h, under conditions that were as normal as possible. A series of measurements was carried out on each of 15 subjects, with at least nine occlusal surfaces restored with dental amalgam, and on five subjects without any amalgam restorations. The subjects had to follow a standardized schedule for 24 h, whereby they ate, drank, and brushed their teeth at pre-determined time periods. The amount of mercury vapor released per time unit was measured at intervals of 30-45 min by means of a measuring system based on atomic absorption spectrophotometry. None of the subjects was professionally exposed to mercury, and all of their amalgam fillings were more than one year old. Study casts were made for each subject, and the area of the amalgam surfaces was measured. Samples of urine and saliva were analyzed so that values for the mercury concentrations and the rate of release of mercury into saliva could be obtained. The average frequency of fish meals per month was noted.(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: Children who chewed gum had a significantly lower net progression of decay (progressions-reversals) over a 24-month period than did the controls and results for the plaque index were in agreement with those of the DMF(S) increment and the net progress of decay.
Abstract: The effect of chewing gum containing xylitol on the incidence and progression of dental caries was tested in a sample of 274 children, aged eight and nine years, of low socio-economic status and high caries rate. They were divided into two experimental groups (15% and 65% xylitol chewing gum distributed three times a day at school) and one control group (without chewing gum). The three groups were exposed to the same basic preventive program. Children who chewed gum had a significantly lower net progression of decay (progressions-reversals) over a 24-month period than did the controls. Results for the two groups chewing gum were similar. Chewing xylitol gum had a beneficial effect on the caries process for all types of tooth surfaces, and especially for bucco-lingual surfaces. The two experimental groups had a DMF(S) increment of 2.24 surfaces, compared with 6.06 surfaces for the control group. For this indicator, there was no difference between the two experimental groups. Results for the plaque index were in agreement with those of the DMF(S) increment and the net progression of decay.
TL;DR: It was concluded that any dissolution of enamel is caused by an undersaturation with respect to enamel apatite, and it was observed that different areas of the enamel surface possess different degrees of resistance.
Abstract: The aims of the present survey were to describe some aspects of (a) enamel solubility in relation to pH and to the fluoride concentration, (b) chemical changes which occur during enamel dissolution, and (c) enamel resistance with an attempt to relate chemical events to clinical observations. The solubility of enamel powder increases dramatically with a decrease of pH. As long as the fluoride concentration in solution is high, the amount of enamel dissolved is low. When fluoride occurs only in the solid phase, the solubility is only slightly affected. Two clinically distinct lesions have been described in dental enamel: the erosion lesion, characterized by a dissolution of enamel from the surface; and the caries lesion, in which the enamel surface layer, accumulating fluoride, remains relatively intact, while the subsurface enamel dissolves. It was concluded that any dissolution of enamel is caused by an undersaturation with respect to enamel apatite. When whole enamel dissolves, the saturation with respect to fluorapatite determines whether a well-mineralized surface layer remains, i.e., whether the dissolution results in an erosion or a caries lesion. The degree of supersaturation with respect to fluorapatite determines the uptake of fluoride in the surface layer and its mineral content. It was observed that different areas of the enamel surface possess different degrees of resistance. A satisfactory explanation for the resistance has not been given.
TL;DR: The results indicate that a high degree of correlation can exist between color-difference measurements regardless of the design of the instrument-measuring geometry, suggesting that the development of clinically useful devices need not be restricted to more traditional integrating-sphere-type designs and that more photometrically efficient alternative designs should be explored.
Abstract: Recent developments in optical electronic instrumentation for color control have made the potential use of clinical photometric analysis a future possibility for dental materials selection and custom restoration design. The development of such instrumentation will require a more complete understanding of the performance of current technologies on translucent materials. This study was designed to evaluate the effects of instrument-measuring geometry on color-difference assessments made on dental porcelains. The results indicate that a high degree of correlation can exist between color-difference measurements regardless of the design of the instrument-measuring geometry. This work suggests that the development of clinically useful devices need not be restricted to more traditional integrating-sphere-type designs and that more photometrically efficient alternative designs should be explored.
TL;DR: Assuming a continuing decline in dental caries, the majority of such populations will benefit most from the use of topical fluorides, however, in high-risk groups, supplementation of pre-emptive fluoride can still be of major importance.
Abstract: A longitudinal study of children from ages 7 to 18 showed that, if enamel lesions were included, the overall number was the same in fluoridated and non-fluoridated areas. However, a significant reducing effect of pre-eruptive fluoride could be seen in the number of dentinal lesions in a fluoridated area, provided that fluoride was also consumed post-eruptively for a considerable period of time. A precise estimation of both pre- and post-eruptive effects was obtained when teeth were classified according to their eruption time as related to the onset of water fluoridation. About 66% of the greatest reduction in pit and fissure caries came from pre-eruptive fluoride, while in smooth surfaces, this effect was reduced to 25%. In approximal surfaces, the reduction was due half to pre- and half to post-eruptive fluoride. Post-eruptive fluoride became more important with decreasing severity of caries attack. Thus, assuming a continuing decline in dental caries, the majority of such populations will benefit most from the use of topical fluorides. However, in high-risk groups, supplementation of pre-eruptive fluoride can still be of major importance.